1. Field of the Invention
This invention relates to a manufacturing method for a piezoelectric, on-demand ink jet recording head wherein thin film piezoelectric elements are used as drive sources for ink ejection, and particularly to an ink jet recording head manufacturing method wherewith lithographic steps are eliminated from the thin film piezoelectric element manufacturing step.
2. Description of the Related Art
One type of ink jet recording head is the piezoelectric, on-demand type wherein a thin film piezoelectric element that functions as an electromechanical conversion element is used as the drive source for ink ejection. Such an ink jet recording head is configured so that ink is stored in a pressure chamber formed in a pressure chamber substrate, changes are imparted to the internal capacity of the pressure chamber via a vibration plate by the mechanical displacement of the thin film piezoelectric element, and ink droplets are jetted from a nozzle hole.
In FIG. 16 is given a diagonal view of the main parts of an ink jet recording head. Part of this diagonal view is rendered as a cross-section to make it easier to understand. As diagrammed in this figure, the ink jet recording head comprises main parts configured such that a vibration plate 2 and thin film piezoelectric elements 5 are provided on one side, while a pressure chamber substrate 1 having pressure chambers 11 formed integrally therein and a nozzle plate 6 whereon are arranged nozzle holes 61 are joined on the other side. In the pressure chamber plate 1, multiple pressure chambers 11 for jetting ink are provided in a strip-like connected row arrangement with separating side walls 12 by etching a monocrystalline silicon substrate or the like. Each pressure chamber 11 connects to a common flow path 14 via an ink supply port 13. In the nozzle plate 6 are formed nozzle holes 61, for jetting the ink, in correspondence with the pressure chambers 11.
The vibration plate 2 has a two-layer structure comprising a lower electrode and an insulating film. In the structure diagrammed in FIG. 16, the lower electrode functions as the lower electrode for the plurality of thin film piezoelectric elements 5, wherefore it is also called the common electrode. Platinum, iridium, and alloys thereof are commonly used for this lower electrode. A silicon dioxide film is commonly used for the insulating film. The thin film piezoelectric elements 5 are formed at positions corresponding to the pressure chambers 11 on the vibration plate 2. An ink tank port 21 is also formed on the vibration plate 2, at a place corresponding to the common flow path 14.
Such a thin film piezoelectric element 5 generally has a structure comprising a piezoelectric film formed from a polycrystalline material, and an upper electrode and lower electrode placed on either side of the piezoelectric film. For the composition of this piezoelectric film is generally used either a two-component system having lead zirconium titanate (hereinafter xe2x80x9cPZTxe2x80x9d) as the main component, or a three-component system to which a third component is added to the PZT of the two-component system. In the configuration of the ink jet recording head, the output terminals of a drive circuit (not shown) are connected to the upper electrode of each thin film piezoelectric element 5, and the ground terminal of the drive circuit is connected to the lower electrode.
In the configuration of this ink jet recording head, if the drive circuit is driven and a prescribed voltage is applied to the thin film piezoelectric element 5, a volumetric change is induced in the thin film piezoelectric element 5, whereupon the ink pressure inside the pressure chamber 11 rises. When this ink pressure rises, ink droplets are jetted from the nozzle hole 61.
Conventionally, lithographic steps have been employed in manufacturing ink jet recording heads. More particularly, it is easy to make elements thereby because the desired pattern can be produced in the thin film piezoelectric elements by a lithographic step. For this reason, lithographic steps have been widely used in the manufacture of ink jet recording heads.
This is now described with reference to FIG. 18. This figure represents a simplified form of a conventional ink jet recording head manufacturing step. The drawings correspond to the Axe2x80x94A cross-section in FIG. 16.
First, as diagrammed in FIG. 18(a), a lower electrode is formed at a film on the monocrystalline silicon substrate 1 on the surface whereof is formed a silicon dioxide film by a thermal oxidation method or the like, whereby the vibration plate 2 is formed having a two-layer structure of an insulating film and lower electrode. Following that, the piezoelectric film 3 and upper electrode 4 are formed as films. Then, as diagrammed in FIG. 18(b), a resist is applied and a prescribed pattern is exposed and developed to form a resist pattern 91. As diagrammed in FIG. 18(c), the upper electrode 4 and piezoelectric film 3 are etched, using the resist pattern 91 as a mask, and the resist pattern 91 is stripped away. In this step the thin film piezoelectric elements 5 are formed. As diagrammed in FIG. 18(d), after forming an etching-protection film (not shown) on the thin film piezoelectric elements 5, resist is applied to the side of the substrate 1 on which the thin film piezoelectric elements 5 are formed and on the opposite side thereof, and a prescribed pattern is exposed and developed to form a resist pattern 92. As diagrammed in FIG. 18(e), using this resist pattern 92 as a mask, the substrate 1 is subjected to wet anisotropic etching with an aqueous solution of potassium hydroxide, for example, to form the pressure chambers 11. As diagrammed in FIG. 18(f), the nozzle plate 6 wherein are formed nozzle holes 61 at positions corresponding to the pressure chambers 11 is bonded by an adhesive 7 to the substrate 1. By the step described above, the ink jet recording head can be fabricated.
With the manufacturing method described above, however, the thin film pressure chambers are formed by lithography, wherefore, while a plurality of thin film pressure chambers can be obtained with one patterning, much material is wasted and costs are increased. Equipment costs are also high, and the equipment requires considerable space. These are problems. With the development in recent years of personal computers, the use of ink jet printers is rapidly proliferating. In view of this situation, cost reduction becomes a necessary and indispensable factor in promoting further proliferation of ink jet printers.
That being so, an object of the present invention is to provide a method wherewith thin film piezoelectric elements and ink jet recording heads can be manufactured inexpensively, in a simple fabrication step, wherein no lithographic step is employed. Another object of the present invention is to provide a forming plate for fabricating thin film piezoelectric elements, and a method of fabricating those forming plates, for use in this manufacturing method. Yet another object of the present invention is to provide an ink jet recording head and an ink jet printer obtained with this manufacturing method.
The thin film piezoelectric element manufacturing method of the present invention is a method wherein the thin film piezoelectric elements are formed by transfer using a forming plate whereon concavities are formed that match the shape of the thin film piezoelectric element. Using this method, it is possible to form the thin film piezoelectric elements by transfer using the forming plate, wherefore the lithographic steps can be eliminated. The forming plate can be used repeatedly, moreover, wherefore manufacturing costs can be lowered.
More specifically, in the concavities noted above, a first electrode and piezoelectric film are sequentially laminated, a second electrode is formed as a film on the piezoelectric film to form the thin film piezoelectric elements, and then the thin film piezoelectric elements are removed from the concavities. At this time, by forming the thin film piezoelectric elements by transfer using a forming plate wherein the side walls of the concavities have a tapered shape, the thin film piezoelectric elements can readily be removed from the forming plate.
This thin film piezoelectric element transfer-forming technology can be applied to ink jet recording head manufacturing step. An ink jet recording head comprises a configuration wherein are provided, on a pressure chamber plate, thin film piezoelectric elements which function as ejection drive sources for the fluid with which are filled pressure chambers formed in the pressure chamber plate. The ink jet recording head manufacturing method of the present invention forms those thin film piezoelectric elements by transfer in a pressure chamber plate using a forming plate wherein are formed concavities matched to the shape of the thin film piezoelectric elements. Moreover, using the forming plate wherein are formed the concavities matched with the shape of the thin film piezoelectric elements, the pressure chamber plate can also be formed by transfer.
The method of fabricating the forming plate for manufacturing the thin film piezoelectric elements of the present invention is one wherein a resist layer is applied to a forming plate mother material, and this resist layer is formed in a pattern matched to the shape of the thin film piezoelectric elements. The forming plate mother material is then etched, using the resist layer on which the pattern is formed as a mask, and the concavities described above are formed. In this case, it is preferable that the openings of the concavities be formed larger than the bottoms thereof, and that the side walls thereof be formed in a tapered shape. It is also desirable that the forming plate mother material be configured from a material such as silicon or quartz. This is because it is easy to perform the fine detailed steping by applying semiconductor technology.
The thin film piezoelectric elements of the present invention are obtained by the manufacturing method described in the foregoing, and exhibit a side shape that is tapered.
The ink jet recording head of the present invention is an ink jet recording head wherein thin film piezoelectric elements are comprised in a pressure chamber plate for functioning as drive sources for jetting the ink with which the pressure chambers formed in that pressure chamber plate are filled, the side shape of which thin film piezoelectric elements are tapered.
The forming plate for manufacturing the thin film piezoelectric elements of the present invention comprises concavities formed in a pattern matched with the shape of the thin film piezoelectric elements. These concavities are formed with an alignment pitch of 70.5 xcexcm, for example. The concavities, moreover, are arrayed in a plurality of rows with a gap of 141 xcexcm between the rows.